What phones are the Duo and Nano compatible with?

Note: The Duo plugs directly into your iPhone's lightning port. But if you're using a Nano you'll need the official Apple Lightning to 3.5mm headphone jack adapter for iPhone 7 and newer! If your phone didn't come with one, you can buy them from Apple's website here, or your local Apple store brand new for $9. Note, 3rd party adapters from Amazon usually don't work!